Cleaning laser tube? And some alignment observations

(Steven Whitecoff) #1

Doing a little quick maintenance which made me realize that I need to clean my mirrors etc MUCH more often than I though. Which got me to thinking, I’ve not seen any mention of cleaning the laser tube itself. A quick test with a Q-tip revealed it was in fact dirty. So if anyone is cleaning theirs, any tips for a good method?

Observations- having aligned my system(long ago) and now ordering up some SI mirrors/lens it occurs to me the HOW TO info I’ve seen is missing the mark in several areas. First I wonder just how important it is to obsess with hitting the dead center of a flat mirror, I can’t think of any valid reason, as long as you never get off to the edge where the laser beam might hit the carrier of course.
Second, IF we still want to hit dead center, seems to me using a card in front or tape etc on the mirror holder and centering on that WILL NOT result in hitting the mirror center, look at what happens as you move the target out from the mirror, draw a picture of this if you can’t visualized it.
Also burn thrus on the target will be depositing soot on the mirror(yes I know the idea is to use enough material on the target so as NOT to burn thru, but it happens). So what is needed are mirror sized, same thickness, disks to go in place of the mirror as aiming targets. This eliminates the soot and will show the true impact point.

(Claudio Prezzi) #2

I wouldn’t touch the tubes output mirror with anything. Just blow clean air on it from a airspray (can). This mirror can not be replace when scrached and would produce bad distortion.

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(Don Kleinschnitz Jr.) #3

Here is what RECI says:

"Do not clean the exterior surface of the output widow mirror with tools such as tampon; otherwise the output power will be seriously affected. The followings are the designated methods to clean up pollution in the exterior surface of window mirror:

1) When the mirror is polluted, do not turn on the laser.

2) Blow the mirror surface sideways with an air blower.

3) Spray the pure alcohol on the mirror surface with sprayer.

4) Turn on the laser after the alcohol gets fully volatilized.

5) If the methods above don’t work effectively, it is necessary to ask for the professional to use tampon with alcohol to clean the mirror surface from middle to edge. The best solution is to prevent the window from being polluted."

Attention: it is forbidden to clean the mirror with acetone.

(Stephane BUISSON) #4

You don’t need to be dead on mirrors center, what you want is to be perfectly square 90° and pararelle/perpendicular to the gantry. That start with a good tube positioning. If it happen to be in the mirrors center it would be a plus for heat dissipation, but being square will provide constancy on all work area.

(Steven Whitecoff) #5

Thanks. To minimize deposits I have taped up the cabinet so air is pulled in from the back side more and with less intake area the flow is much stronger so hopefully smokey cut wont overwhelm the extraction blower any more. Dont know why the cabinet has a big hole in the bottom but taping it up seems to help a lot.

(Don Kleinschnitz Jr.) #6

Placement of the beam at the mirrors center is not in itself critical. However, off center beams often indicate a larger problem of the beam being not traversing the optical path parallel to the x-y axis of motion (gantry). This can be caused by the tube positioning or maladjustment of any of the mirrors along the path, often both.
I suspect that the root cause of difficult machine alignment is a miss-positioned tube that is attempted to be corrected by one or more mirrors.
In practice there isn’t a lot of room for the beam to be off center on upstream mirrors and still hit the objective lens perpendicular and on center [which is important].

Since the beam is invisible you cannot see how the beam exits the laser and is traversing along the x and y axis and there is no real reference to the gantry of motion. Your only point of reference it when the beam hits a mirror. You have no real idea where the mirror is positioned relative to the gantry of motion. Further you have no idea what angle the beam hits the mirror. If the beam hits the mirror at a compound angle it will reflect that way and you will have to try and counter it by adjusting the mirror in the opposite direction.

I got tired of fighting the above problem. That is what prompted me to replace my mirrors (for stability) and build some alignment tools that provided more visibility and repeat-ability into the alignment process.
These tools have the side benefit of not touching and minimally contaminating mirror surfaces. I always clean the optics after an alignment anyway.

There are 4 posts that pertain to improving K40 optical components and alignment:
Improving mirror #1
Improving mirror #2
K40 optical alignment tool theory & design
Using K40 alignment tools

(Don Kleinschnitz Jr.) #7

I think you want laminar flow across the object for best operation, for this reason most insure that air is brought in the front and out the back. In my case I lifted the lid slightly but plan to open a slot in the front some day.

I think the hole in the bottom was an attempt at an air input port.

Are you using the stock evacuation fan, I found it to be woefully inadequate and I run a much larger fan. I initially had my machine in my den and never could control the fumes with the stock setup.

Now I have a lot of airflow (440cfm) into a 6" pipe duct-ed through a window.

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(Stephane BUISSON) #8

You may have notice the tube compartment is not vented, you can reduce fume going near the tube by reducing the laser ray hole after calibration.

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(Don Kleinschnitz Jr.) #9

Never thought about that. How about a positive pressure muffin fan. For some time I have been thinking about cooling the exterior of the tube anyway. I think @HalfNormal or @HP_Persson does this?

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(0.45 NACL) #10

I reversed the exhaust fan on my K40 to positive-pressure the electronics compartment.

(Steven Whitecoff) #11

Got new mirrors today and of course they are approx. 50% thicker so my days old alignment check is no longer valid.
I like the idea of a fan for the tube compartment, I should have either a pancake or CPU fan that could be fitted. If we push air into the laser compartment, it can exit thru the hole into the cutting compartment, aided by the exhaust fan.